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Construction Of Keggin-type Polyoxometalate-based Open Frameworks And Their Photocatalytic Property

Posted on:2016-04-24Degree:MasterType:Thesis
Country:ChinaCandidate:H F HaoFull Text:PDF
GTID:2191330464957487Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Microporous materials have been rapidly developed in recent years. In this research field, metal-organic frameworks(MOFs) are of great interest not only due to their diversity of components and structures, but also their wide applications in catalysis, gas-storage, detection and biomedicine. The design and synthesis of MOFs based on polyoxometalates(POMs) have attracted considerable attention in recent years. The introduction of POM units, acting as not only templates but also nodes and pillared units, has dramatically enriched the family of MOFs. These compounds have merged the merits of POMs and MOFs, and can potentially be applied in heterogeneous catalysis, selective absorption, electronic and magnetic materials. Especially in the field of catalysis, dispersing catalytically active POM units into MOFs can not only keep the integrity of POM anions and improve the catalytic activity, but also realize the recovery of catalysts by reducing the solubility.POMs, transition-metal(TM) ions, and neutral N-donor ligands(L) are three elemental building units to construct and determine the final structures. Usually, the Keggin-type POM is priority because of their stability and strong catalytic activity. TM cations are important nodes because of the explicit coordination geometries, the lower charge numbers, and the similarity of coordination ability at linking oxygen atoms from POMs and organic ligands. Neutral N-donor bridging ligands have been widely chosen in exploring new POM-based metal-organic open frameworks.Based on aforementioned consideration, we attempt to explore new POM-based MOFs with Keggin-type POM units, TM cations and rigid briding N-donor ligand 1,4-bis(1-imidazolyl)benzene(bimb). In this thesis, five new hybrid compounds have been hydrothermally synthesized:[H2L][Cu L][Si W12O40]·2H2O(1)[H2L]4[Co L(H2O)3]2[Si W11 Co O39]2·12H2O(2)[Cu L]2KH[Si W11 Co O39(H2O)]·2H2O(3)(Cu L)4[Ge W12O40]·H2O(4)(Cu L)2K[HSi Mo12O40]·6H2O(5)(L=1,4-bis(1-imidazolyl)benzene(bimb)).All these compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1, 3 and 5 present a 3D open-framework, and compounds 2 and 3 display a 2D layer. According to the synthetic progress and structures of compounds 1-5, it is found that high p H of synthetic system, high negative charge of POM units, and high coordination mode of TM centers, may tend to construction of 3-D MOFs. The photocatalytic properties of compounds 1-4 were also investigated by degradating methylene blue(MB) under UV light. All compounds showed good catalytic activity and structural stability. The possible catalytic mechanism was discussed based on the active species trapping experiments. The difference of the photocatalytic activities of compounds 1-4 were explained by the comparison of band gap structures of different POM species and the packing modes of POM units in different hybrid compounds.
Keywords/Search Tags:Keggin-type, Polyoxometalate, Metal-organic framework, Photocatalysis, Rigid ligand
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